Will getting a better Graphics Card Help with Frame rate issues?
Yes, with Nvidia you can render using GPU and also you can use it for OpenSubdiv compute.

Is not true that computed device is only for rendering. GPU is used also for drawing viewport using OpenCL.
Only if you have 2 and more graphics cadrs, one is marked as "(Display)" this card is used for drawing viewport, other ones are only for rendering (and preview render in viewport)

BTW: for 400USD I highly recommend Nvidia 1070. The best ratio speed/price/power comsumption and 8GB VRAM allow you to render complicated scenes without "CUDA: out of memory error". 

EDIT: one important thing here: if you have very slow CPU, fast GPU don't raise fps too much, because they must work synchronized. CPU is "the boss" and send calls to GPU. Other words: CPU must tell to GPU what is going on and GPU work with this data.